Centrifugal classifier

ABSTRACT

A HOUSING HAVING A CYLINDRICAL CAVITY THEREIN WITH A ROTOR COAXIALLY MOUNTED FOR ROTATION RELATIVE THERETO AND PASSAGEWAYS FOR PROVIDING A FLOW OF AIR FROM THE OUTER CIRCUMFERENCE TO THE AXIS OF THE ROTOR. A PLURALITY OF RADIALLY ORIENTED LONGITUDINALLY EXTENDING FINS AFFIXED TO THE ROTOR FOR PRODUCING A FORCED VORTEX IN THE FLOW OF AIR AND A PLURALITY OF RADIALLY SPACED SLOTS IN EACH OF THE FINS COINCIDING WITH LONGITUDINALLY EXTENDING RODS AFFIXED TO THE HOUSING FOR PRODUCING SHEAR FORCES TENDING TO DISPERSE SOLIDS CARRIED BY THE AIR INTO DISCRETE PARTICLES WHICH CAN BE SEPARATED INTO COARSE AND FINE FRACTIONS BY CENTRIFUGAL FORCE WITHIN THE VORTEX.   D R A W I N G

March 13, 1973 c:. E. LAPPLE CENIRIFUGAL CLASSIFIER Filed Ju 1y 10. 1970 2 Sheets-Sheet 1 INVENIOR. CHHRLES E. LHPPLE l LL GOULD fTTOF-NEYS MERCHRNT March 13, 1973 LAPPLE 3,720,313

CENIRIFUGAL CLASSIFIER Filed July 10. 1970 v 2SheetS-Shet 2 1NVENTOR. CHRRLES E. LHPPLE I NERCHHNT 9 Gouu3 United States Patent Ofifice 3,720,313 Patented Mar. 13, 1973 3,720,313 CENIRIFUGAL CLASSIFHER Charles E. Lapple, Los Altos Hills, Calif., assignor to Donaldson Company, Inc., Minneapolis, Minh. Filed July 10, 1970, Ser. No. 53,845 Int. Cl. B07b 7/083 U.S. Cl. 209-144 20 Claims ABSTRACT OF THE DISCLOSURE A housing having a cylindrical cavity therein with a ro tor coaxially mounted for rotaton relative thereto and passageways for providing a flow of air from the outer circumference to the axis of the rotor. A plurality of radially oriented longitudinally extending fins afiixed to the rotor for producing a forced vortex in the flow of air and a pluralty of radially spaced slots in each of the fins coinciding with longitudinally extending rods afiixed to the housing for producing shear forces tending to disperso solids carried by the air into discrete particles which can be separated into coarse and fine fractions by centrfuga] force within the vortex.

BACKGROUND OF THE INVENTION Field of the invention.The present invention pertans to apparatus for classifying powders and the like. Classification in general is the separation of a powder into a coarse fraction containing coarse particles, having a size equal to or somewhat larger than a cut size, and a fine fraction containing fine particles having a size equal to or less than the cut size. The cut size is equivalent to the separation point or the particular size of partcles about which the powder is separated.

Description of the prior art.-The present centrifugal classifier is an improvement over the centrfuga] classfier described in Pat. No. 3,491,879, issued Jan. 27, 1970, to the same inventor. In the prior art centrifugal classifier described in the above-identified patent, a rotor is mounted for rotaton Within a hollow stator so they are separated by a narrow annular air gap. The rotor has a hollow coaxial chamber therein in communication with the air gap along the periphery of the rotor, and a central coaxial opening for the egress of an elutriating fluid and the fine fraction of the powder. The elutriating fluid is supplied, by means of a pressure diterential, to the chamber through the gap and a vortex is produced generally Within the rotor in the flow of fluid by the rotaton of the rotor. The powder to be classified is supplied to the vortex and the coarse fraction of the powder, which is forced toward the stator, is removed through a coarse fraction passageway while the fine fracton is removed with the fiuid through the axial opening in the rotor.

Dspersion of the partcels making up the powder, or solid material, is accomplished in this prior art apparatus by the elutriating fiuid flowing from either side of the narrow annular air gap longitudinally inwardly toward the periphefal opening of the chamber in the rotor. The powder enters the air gap through the stator along a radius of the chamber so that the elutriating fiuid and the powder initially enter the air gap traveling perpendicular to each other. In this prior art structure the air gap is constructed relatively narrow so that the elutriating flud is traveling at a relatively high speed. Further, the course partcles are required to travel nearly the full length of the air gap from the solids inlet to reach the coarse particle outlet. Thus, disperson of the solid into discrete particles is provided.

SUMMARY OF THE INVENTION The present invention pertains to a centrifugal classifier of the type having a rotor mounted within a chamber con structed so that a vortex of elutriatng fluid is formed therein, including means for producing shear forces on solids carried by the elutriating fiuid generally radially along the rotor to disperse the solids into discreto particles.

It is an object of the present invention to provide a new and improved centrifugal classifier.

It is a further object of the present invention to provide a centrifugal classifier utilizing new and improved apparatus for dispersing solids, such as powders and the like, into discrete particles.

These and other objects of this invention will become apparent to those sklled in the art upon consideration of the accompanying specificaton, claims and drawings.

BMEF DECRIPTION OF THE DRAWINGS Referring to the drawings, wherein like characters indicate like parts throughout the figures:

FIG. 1 is a view in side elevation of the rotor-stator assembly, portions thereof broken away and shown in section;

FIG. 2 is a sectional view as seen generally from the irregular line 22 in FIG. 1; and

FIG. 3 is a sectional view as seen generally from the irregular line 33 in FIG. 1, portions thereof removed.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the numeral 10 generally designates a main body having an elutrating fluid passageway ll, a solids inlet passageway 12, a coarse fraction outlet passageway 13, and a conduit 14 attached to a notor 15 for rotatably mounting the rotor 15 and serving as an outlet passageway for elutriating fluid and a fine fraction. No material sources or collecting apparatus are illustrated in connection with the various passageways 11, 12 and 13 and the conduit 14 and no apparatus for mounting the body 10 or rotating the rotor '15 are illustrated or described in this embodiment because the main body 10 of the present centrfuga] classifier could be substituted for the main body 10 in the centrifugal classifier described in Pat. No. 3,491,879. Therefore, for purposes of describing a complete centrifugal classifier, the various components illustrated and described in the aboveidentified patent are incorporated in the present application by this reference. Further, while these various components are incorporated for exemplary purposes, it should be understood that many other types of devices might be substituted for those illustrated as long as they provide the functions described in the abovementoned patent.

In the present embodiment of the main body 10 a stator or housing 20 includes a first member 21 having a generally circular cross section with a dish-like cavity 22 opening axially outwardly on one side thereof. A second member 23 is fixedly attached over the opening of the cavity 22, by some means such as screws or the like, to completely enclose the cavity zz, except for the various passageways 11, 12, 13 and the conduit 14. The conduit 14 extends through the second member 23 generally coaxial with the housing 20 and is rotatably mounted in the second member 23 by means of a sealing bearing 24. The sealing bearing 24 prevents the egress of olutriating fluid from the cavity 22 around the conduit 14 and also incorporates a thrust-type bearing to prevent axial movement of the conduit 14.

The rotor 15 includes two parallel spaced apart plates 30 and 31 afiixed to the conduit 14 within the cavity 22 for rotation therewith. The plate 30 is positioned parallel With and in juxtaposition to the inner surface of the second member 23 and the plate 31 is spaced axially therefrom and generally within a depression in the axially directed surface of the cavity 22. A plurality of circumferentially spaced fins 32 and 33 are affixed between the plates 30 and 31 in generally radially oriented longitudinally, or axially, extending relationship. The diameter of the plate 30 is substantially greater than the diameter of the plate 3=1 and the fins 32 extend from adjacent the outer surface of the conduit 14 to adjacent the outer periphery of the plate 30. The fins 33 extend radially from adjacent the outer periphery of the plate 30 approximately midway to the outer surface of the conduit 14. Thus, a substantial portion of the edges of the fins 32 and 33 opposite the plate 30, located generally radially outwardly from the plate 31, lies adjacent the inner surface of the cavity 22. In the present embodiment, the rotor 15 is constructed by positioning the edges of the fins 32 and 33 in radially extending slots formed in the inner surface of the plate 30* and the plate 31 is affixed to the plate 30 by means of bolts or the like. The conduit 14 has a plurality of openings 35 therein oriented to provide communication between the inner passageway of the conduit 14 and the area between the plates 30 and 31 of the rotor 15.

The inner surface of the cavity 22 extends from the central depression, described briefly above, outwardly generally parallel with the exposed edges of the fins 32 and 33 to a generally cylindrical wall 40. While the entire inner wall of the cavity 22 is cylindrical within the mean ing of the term, the portion 40 is constructed so that coarse particles thrown outwardly by centrifugal force will be directed into the coarse fraction outlet passageway 13 thereby. It should be understood that modifications and variations of the cavity 22 may be devised by those skilled in the art and the present configuration is simply for exemplary purposes.

The dished format of the cavity in 22 represents an attempt to compensate for the variation of centrifugal force with radial position. As the radius becomes smaller, centrifugal force becomes less. To maintain a constant cut size it, therefore, becomes necessary to reduce inward gas velocities a corresponding amount. This inward gas velocity is reduced by enlarging the air flow passage height, which results in the dished surface. The form of the dished surface (or even its presence) is not essential to the spirit of this invention. Not having a dished surface would result in a simpler device, but could result in some loss of sharpness of classification because of the variable cut size with radial position.

Each of the fins 32 and 33 has a plurality of radially spaced-apart longitudinally extending slots 45 formed therein and openings at the edge adjacent the inner wall of the cavity 22. A plurality of radially spaced apart, longitudinally extendng rods 46 are afiixed in the inner wall of the cavity 22 adjacent the fins 32 and 33 so as to coincide with the slots 45 in the fins 32 and 33 during rotation of the rotor 15. Thus, large shear forces are produced in the vortex during rotation of the rotor 15 because of the movement of the fins 32 and 33 relative and proximate to the rods 46. It should be understood that rotating fins 32 and 33 and stationary rods 46 are utilized in this embodiment for exemplary purposes and high shear forces in a vortex might be produced in a variety of ways, for example forming a rotor comprised of two halves, each of which is equipped with radially oriented vanes intermeshing and rotating in opposite directions, providing annular rows of screens or vanes (in place of the rods 46), providing some combination of these embodiments, etc.

The solids inlet passageway 12 is formed in the first member 2 1 of the housing so as to extend longitudinally through the first member 2 1 and communicate with the cavity 22 adjacent the innermost rods 46. Thus, the fine particles of solids injected into the centrifugal classifier through the solids inlet passageway 12 travel inwardly toward the openings 35 while the coarse particles travel outwardly and are subjected to the shear forces produced by the rods 46. Any group of fine particles which tend to cling together and appear to the classifier as a coarse particle are dispersed into discrete particles by the shear forces produced by the cooperation of the fins 32 and 33 and the rods 46. Once the particles are dispersed into discrete particles, the vortex acts upon them according to their individual characteristics (weight, size, etc.) and they continue to move outwardly if they are above the cut size of the classifier, or they turn and progress inwardly toward the opening 35, if they are below the cut size of the classifier. The coarse particles travel along the cylindrical Wall 40 on the cavity 22 until they reach the coarse fraction outlet passageway 13 whereupon they egress from the cavity 22 and are collected. The fine particles and the elutriating fluid pass through the openings 35 and out the conduit 14 where the fine particles are collected and the elutriating fluid is rejected or recirculated. Thus, the members including fins 32 and 33 produce a vortex in the cavty 22 and the members, including the rods 46, produce high shear forces Within the vortex which disperse solids carried by the elutriating fluid into discrete particles so that they can be properly classified. Because of the high dispersion in the present centrfuga] apparatus, the sharpness of separation of particles is improved without greatly affecting the cut size and other characteristics of the classifier.

In a modification of this invention, previously mentioned, utilizing two intermeshing rotors revolving in opposite directions, the solids inlet passageway 12 would be located at the center of a hollow shaft in the second rotor. The solids would then be led outwardly radially within the second rotor to a radial position corresponding to that occupied by passageway 12 in the embodiment shown in FIG. 1, at which point it would empty into the space between the two rotors as in FIG. 1.

While I have shown and described a specific embodiment of this invention, further modifications and improvements will occur to those skilled in the art. I desire it to be understood, therefore, that this invention is not limited to the particular form shown, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of this invention.

I claim:

1. A centrifugal classifier adapted to centrifugally separate particles into coarse and fine fractions, comprising:

(a) a housing having a cavity therein defining a gen erally cylindrical inner wall formed about a longitudinally extending axis;

(b) rotor means, having an outer periphery thereof positioned adjacent said inner wall, mounted in said cavity for rotation about said axis, said axis extending through a center of said rotor means;

(o) a plurality of longitudinally extending, radially separated first dispersing members mounted within said cavity;

(d) a plurality of longitudinally extending, radially separated second dispersing members mounted within said cavity;

(e) one of said plurality of first and second members being afifixed to said rotor means for rotating said one plurality relative to the other plurality about said axis, said first and second members intermeshing to allow relative rotation therebetween;

(f) an axial outlet opening in said housing in communication with the cavity adjacent said center of said rotor means;

(g) an elutriation fluid inlet in said housing adjacent said outer periphery of said rotor means to provide a flow of fluid radially inwardly over said rotor means, said rotor means when rotating forming a fluid vortex in a zone including said first and second members to centrifugally separate solids particles introduced therein;

(h) a solids inlet passageway in said housing positioned to supply, directly into said intermeshing members, the particles to be classified into coarse and fine fractions, said first and second dispersing members providing shear forces to disperse said particles prior to the particles being centrifugally separated by said vortex; and

(i) a coarse fraction outlet passageway in said housing adjacent said periphery of said rotor means for receiving the coarse fraction of solids, the elutriating fluid and the fine fraction egressing through said axial outlet opening.

2. A centrfuga] classifier as set forth in claim 1 wherein the plurality of first members include radially extending fins each having a plurality of radially spaced apart, longitudinally extending slots therein to intermesh with said plurality of second members.

3. A centrfugal classifier as set forth in claim 2 wherein the plurality of second members include radially spaced apart, longitudinally extending rods having a radial di mension slightly smaller than the radial dimension of the slots in the fins and positioned to coincide with the slots during rotation.

4. A centrifugal classifier as set forth in claim 3 wherein the fins are connected to the rotor means for rotation therewith.

5. A centrfuga! classifier adapted to separate particles into coarse and fine fractions, comprising:

(a) a housing having a cavity therein defining an inner wall formed about a longitudinally extending axis;

(b) a rotor mounted for rotation about is center and said axis within said cavity, said rotor having a plurality of radially separated, longitudinally extending fins attached thereto for rotation therewith, and having an outer periphery thereof positioned adjacent said inner wall;

(o) fluid inlet passageway means in said housing outward of said fins for providing a flow of elutriating fluid into said cavity;

(d) a solids inlet passageway in said housing adjacent said fins;

(e) a coarse fraction outlet passageway in the inner wall of said housing;

(f) an axially located fine fraction and elutriating fluid outlet passageway communicating with the cavity in said housing at said rotor center, the elutriating fluid flowing from the fluid inlet passageway to the fine fraction and elutriating fluid outlet passageway through said fin during rotation of said rotor to produce a vortex and for centrifugally separating in the vortex solid particles introduced into the housing through the solids inlet passageway; and

(g) longitudinally extending pin means affixed within the cavity in said housing, adjacent said solids inlet passageway, and extending between said radially separated fins to produce shear forces to disperse the solids into discrete particles.

6. A classifier for centrifugally separating particles into coarse and fine fractions, comprising:

(a) rotor means having an outer periphery and an axis of rotation at the center thereof;

(b) housing means defining a cavity therein;

(c) means mounting said rotor means in said cavity for rotation about said axis;

(d) an elutriating fluid inlet opening in said housing means adjacent said outer periphery of said rotor means, and an axial outlet opening in said housing means adjacent the center of said rotor means to provide a flow of fluid along a radial path over said rotor means, said rotor means when rotating forming a fluid vortex between said fluid inlet opening and said axial outlet opening and separating particles introduced therein by centrfugal force within the vortex;

(e) a particle inlet passageway in said housing means to introduce the particles to be separated into the vortex, the separated fine fraction being carried with the fluid through said axial outlet opening;

(f) a coarse fraction outlet passageway in said housing means adjacent said periphery of said rotor means; and

(g) a plurality of closely spaced dispersing members mounted in said cavity in said radial path, a first group of said dispersing members being mounted on said rotor means to produce high shear forces with said other dispersing members upon rotation of said rotor means to disperse said particles to facilitate separation thereof.

7. The apparatus of claim 6 wherein said first group of dispersing members comprise fins on said rotor means and said other dispersing members comprise rods mounted on said housing means, and wherein said dispersing members are at least partially disposed between said particle inlet passageway and said axial outlet opening.

8. The apparatus of claim 6 wherein said first group of dispersing members comprise an annular ring of circumferentially spaced fins on said rotor means concentric with the center thereof, and extending from said rotor means generally parallel with said axis, and wherein said other dispersing members comprise an annular concentric ring of axially extending rods on said housing means overlapping said fins.

9. The apparatus of claim 6 wherein said first group of dispersing members comprise at least two annular, radially spaced rings of circumferentially spaced fins on said rotor means concentric with the center thereof and extending from said rotor means generally parallel with said axis, and wherein said other dispersing members extend between said spaced rings of fins.

10. The apparatus of claim 9 wherein said other dispersing members comprise an annular concentric ring of axially extending rods on said housing extending between said spaced rings of fins.

11. The apparatus of claim lll wherein said particle inlet passageway is located generally in said annular ring of rods to thereby discharge the particles to be separated into an intense shear zone between said rings of fins, and wherein said rotor means and fluid provide clasification zones both radially inwardly and radially outwardly of said shear zone.

12. The apparatus of claim 6 wherein said rotor means comprises a pair of spaced, connected parallel plates of different diameter, wherein one of said plates has a central opening leading to said axial outlet opening, wherein said radial path extends between said plates, and wherein said first group of dispersing members are mounted on the larger of said plates and extend axially in the direction of the plane of the smaller plate.

13. The apparatus of claim 12 wherein said first group of dispersing members comprise at least two annular, radially spaced rings of circumferentially spaced fins on said rotor means concentric with the center thereof, said rings having a diameter larger than the diameter of the smaller plate.

14. The apparatus of claim 13 wherein said other dispersing members comprise an annular concentric ring of axially extending rods on said housing means.

15. The apparatus of claim 14 wherein said particle inlet passageway is located generally at said annular ring of rods.

16. The apparatus of claim 6 wherein said first group of dispersing members comprise a plurality of annular, radially spaced rings of circumferentially spaced fins on said rotor means concentric with the center thereof and extending from said rotor means generally parallel With said axis, wherein said other dispersing members comprise a plurality of annular concentric rings of axially extending rods on said housing means, said rings of rods and fins intermeshing to form a plurality of intense shear zones, and an alternate plurality of classification zones in which the centrfuga] separation occurs, said particle nlet passageway being located in said housing to introduce the particles into one of said zones.

17. The apparatus of claim 16 wherein said particle inlet passageway is located generally at the innermost annular ring of rods.

18. A method of separating particles into coarse and finefractions comprising the steps of causing an elutriating fluid to flow radially inwardly through a vaned rotor means from a periphery to an axial outlet thereof, rotating said rotor means at a selected speed to establish centrfuga] forces in said flowing fluid, discharging the particles to be separated into said flowing fiuid such that the centrifugal forces throw the particles above a given cut size outwardly from the rotor means while the smaller particles are carried by said flowing fiuid to said axial outlet, and subjecting substantially all of the particles to be separated to an intense shearing action by passing the particles through closely spaced, intermeshing, alternately fixed and rotating dispersng members located between said periphery and axial outlet in close proximity to the arca in which separation occurs.

19. The method of claim 18 including the step of discharging the particles to be separated directly into an area of intense shearing action to disperse the particles immediately prior to separation thereof.

20. The method of claim 18 including the step of subjecting at least some of the particles to a plurality of a1- ternate shearing actions and separating actions in said rotor means.

References Cited UNITED STATES PATENTS 3,433,422 3/1969 Guenther 209144 X 2,329,900 9/1943 Hermann 209-148 X 2,338,779 1/1944 Mutch 209145 X 3,269,537 8/1966 Kaiser 209144 2,199,015 4/1940 T0ensfeldt 209148 X 2,276,761 3/1942 Carey 209144 2,428,670 10/1947 Hulse 241--188 A FRANK W. LUTTER, Primary Examiner R. J. HILL, Assistant Examiner 

